Some of my favourite Douglas Adams ones:

Let’s think the unthinkable, let’s do the undoable. Let us prepare to grapple with the ineffable itself, and see if we may not eff it after all.

The major problem—one of the major problems, for there are several—one of the many major problems with governing people is that of whom you get to do it; or rather of who manages to get people to let them do it to them. To summarize: it is a well-known fact that those people who must want to rule people are, ipso facto, those least suited to do it. To summarize the summary: anyone who is capable of getting themselves made President should on no account be allowed to do the job.

For a moment, nothing happened. Then, after a second or so, nothing continued to happen.

God’s Final Message to His Creation: 'We apologize for the inconvenience."

Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so.

It can hardly be a coincidence that no language on earth has ever produced the expression, ‘As pretty as an airport.’